Using knives in cast iron pans
I have a fairly recent 12" Lodge cast iron pan that I use weekly to make pizza in.
I cut it in pieces directly in the pan; last week I realized that the knife left slight etched marks on the finish (yeah i just realized the idiocy of it all...)
(Metal spoons/other tools don't leave marks - and i'm pretty brutal with my cookware - so what gives?
Obviously this should affect the seasoning. So should I just remove the whole pizza out of the pan before slicing or is there some kind of knife/contraption I could use that won't scratch the pan?
I agree with Mikie -- just move the pizza to a cutting board, as I always do with my pizzas (cooked on a stone, rather than in a pan).
As for the cast iron, personally I find marks from metal utensils to be rather annoying when they scratch or dig into the seasoning. As Chemicalkinetics said, you will be able to regenerate the seasoning over time, but I personally love my perfectly smooth non-stick surfaces I've generated over the years. I find deep groves from a metal utensil can take months to go away again. I like to be able to slide anything easily around my pan (even omelets and such), so even tiny grooves are a hindrance.
We are talking about the traditional bare cast iron Lodge pan, right? Don't worry about the marks. Seasoning will generate over time. You scrap some, you generate some. Unless, you only use that pan for pizza and cut it with a knife every single time, I don't think it is a big deal.
However, to answer your question specifically, you can always use a plastic knife. I use a plastic knife on my Teflon nonstick bakeware.